The goal of this proposal is to develop a commercial ?plug and play?, user-friendly, powerful and reliable dynamic clamp system, to enable all neuronal electrophysiologists to be able to perform sophisticated dynamic clamp experiments, without any requirement for programming, engineering, or mathematical modeling skills. We will develop hardware and software specifically for neuroscience applications, focusing on the specific stability and reliability needed for routine neuronal electrophysiology. We will focus on the critical combination of software, operating system, and hardware to achieve high speeds, but more importantly high reliability. Problems with timing, interrupts, and stability, were the key concerns and recurrent problems raised in interviews with our potential customers who were using home-made research platforms. Innovations in this proposal include: 1) A digital modulated conductance clamp mode and supporting software that will greatly expand the stability of the system during the rapid voltage changes that occur during neuronal action potentials; 2) The first dynamic clamp system to incorporate real-time Ca2+ transient (and other signaling) as an input. Many currents and related electrophysiological behaviors are sensitive to global Ca2+ levels. We will have the first dynamic clamp system capable of using Ca2+ (and other fluorometric signals) to interact with current amplitudes and gating behavior. This is a major advance in the application of dynamic clamp. 3) This first Markov Model based dynamic clamp system. Many channels are much more accurately modeled using Markov models as opposed to using the older and simpler Hodgkin-Huxley formalism. This is of critical importance in modeling ligand gated binding, Ca2+- dependent behavior and state-dependent drug binding. The three aims of this project are to 1) Develop rectifying background currents for the stabilization of neuronal resting potentials. We will establish a library of rectification models and a spline-driven model derived from user input that can be used in real-time during experiments. 2) Develop a Dynamic Clamp system with two inputs, the standard one for voltage, and an additional input for real time calcium transients in order to simulate channels such as calcium activated potassium channels. 3) Develop digitally controlled conductance clamp for enhanced stability. This aim will automatically prevent, detect, and correct data artefacts arising from the limitations of dynamic clamp methodology, which increases quality control.